Electronic devices commonly utilize piezoelectric, piezo-resistive and capacitive components to measure dynamic changes in mechanical variables such as acceleration, vibration, and mechanical shock. Such measurements are obtained by converting mechanical motion into an electrical signal. These devices are useful for a wide variety of applications including, but not limited to engineering, machine monitoring, biological study, navigation, medical applications, transportation, motion input, orientation sensing, and image stabilization.
One such class of electronic device is the accelerometer, which is capable of measuring acceleration by generating or altering a voltage proportional to a physical accelerative force acting thereon. Piezoelectric accelerometers are operative to convert mechanical force, such as a force applied to a piezoelectric crystal by a seismic mass, to an electrical signal. Piezo-resistive accelerometers use a piezo-resistive sensor element in place of the piezoelectric crystal. When a force acts upon a seismic mass, the stress induced on the piezo-resistive gages causes a change in resistance, thereby altering a voltage provided across the gages of the sensor element. Unlike piezoelectric accelerometers, piezo-resistive accelerometers measure acceleration levels down to zero Hertz (i.e. static conditions).
While these devices are capable of producing accurate measurements when properly calibrated, their baseline voltage outputs (at zero acceleration for example) are subject to drift. Drift may be the result of temperature and/or environmental changes, component break-in, as well as packaging stresses that tend to relax over time. The output bias of a typical accelerometer output may shift, for example, a couple percent of full range as a result of its drift, thereby reducing the measurement accuracy of the device over its lifecycle.
In order to compensate for these errors, manufacturers often employ thermal conditioning techniques in an attempt to work out these anomalies prior to final device calibration. Such techniques include extended burn-in periods and thermal cycling of the devices. However, these techniques do not fully cure the problem. Accordingly, end users either have to allot for these measurement uncertainties or employ separate instrumentation, such as auto-zero signal conditioners, to periodically perform zero correction.
Additional solutions include the implementation of mechanical potentiometers integrated into the circuits of the devices for manually dialing-out this drift. However, potentiometer-based solutions tend to be time consuming and are of limited accuracy. Other devices employ auto-zero algorithms based on ADC-MCU-DAC arrangements (where ADC is analog to digital converter, DAC is digital to analog converter, and MCU is microcontroller unit) which induce digital noise and increase cost.
Accordingly, improved systems and methods of offset voltage correction are desired.